Preparation of plastic-metal products including laminates,composite tubes and the like

ABSTRACT

THIS INVENTION RELATES TO THE PROVISION OF NOVEL AND ECONOMICAL WAY OF: (1) HEAT BONDING, SOLELY WITH HEAT, PLASTICS, PARTICULARLY THE FLUOROCARBON POLYMERS AND SPECIFICALLY THE POLYMER HEXAFLUOROPROPYLENETETRAFLUOROETHYLENE MANUFACTURED EXCLUSIVELY BY E.I. DU PONT DE NEMOURS &amp; COMPANY AND SOLD UNDER THE TRADE NAME OF FEP, TO METAL SURFACES, PARTICULARLY FLEXIBLE METAL SHEETS AND PLATES. (2) HEAT BONDING OR ADHESIVE CEMENT BONDING THESE SAME METAL SHEET-PLASTIC LAMINATES TO OTHER METAL SURFACES, PARTICULARLY THOSE OF PIPES AND VESSELS. (3) FABRICATION OF COMPOSITE TUBES OR SLEEVES, SOLELY BY HEAT BONDING OF SEAMS OF THESE COMPOSITE SHEETS SHAPED INTO TUBES   OR SLEEVES, SAID TUBES OR SLEEVES BEING USEFUL ALONE AS CONDUITS FOR FLUIDS OR WHICH MAY BE HEAT OR ADHESIVE CEMENT BONDED TO OTHER METAL PIPES AND VESSELS, AS PROTECTIVE COATS AND LINERS, AND METHOD AND MEANS FOR INSTALLING SAID LINERS.

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PREPARATION OF PLASTIC-METAL PRODUCTS INCLUDIN LAMINATES, COMPOSITETUBES AND THE LIKE Original Filed May 28, 1970 a Sheets-Sheet UnitedStates Patent PREPARATION OF PLASTIC-METAL PRODUCTS INCLUDING LAMINATES,COMPOSITE TUBES AND THE LIKE Ransome W. Erwin, Houston, Tex., assignorto Austral- Erwin Engineering Co., Houston, Tex.

Original application May 28, 1970, Ser. No. 41,375, now abandoned.Divided and this application Apr. 21, 1972, Ser. No. 246,220

Int. Cl. B2941 23/10 US. Cl. 156--218 17 Claims ABSTRACT OF THEDISCLOSURE This invention relates to the provision of novel andeconomical ways of: (1) Heat bonding, solely with heat, plastics,particularly the fluorocarbon polymers and specifically the polymerhexafluoropropylenetetrafluoroethylene manufactured exclusively by E. I.du Pont de Nemours & Company and sold under the trade name of PEP, tometal surfaces, particularly flexible metal sheets and plates. (2) Heatbonding or adhesive cement bonding these same metal sheet-plasticlaminates to other metal surfaces, particularly those of pipes andvessels. (3) Fabrication of composite tubes or sleeves, solely by heatbonding of seams of these composite sheets shaped into tubes or sleeves,said tubes or sleeves being useful alone as conduits for fluids or whichmay be heat or adhesive cement bonded to other metal pipes and vessels,as protective coats and liners, and method and means for installing saidliners.

This is a division of application Ser. No. 41,375, filed May 28, 1970now abandoned.

PHASE A--IMPROVEMENTS IN COATING METAL SURFACES WITH PLASTIC FILMS ANDARTI- CLES MADE FROM SAME Broadly speaking this phase of the inventionrelates to improvements in method and apparatus for coating metalsurfaces with plastic films and to articles made therefrom.

Current and Past Practices: The use of plastics for coating metalsurfaces for protection against corrosion and abrasion, for lubricity,for minimizing depositions, and for making surfaces preferentially oilwettable is known and practiced. For this purpose use has been made offluoronated polymeric plastic materials such as Teflon, FEP and thelike. Teflon and FEP are trade names of the E. I. du Pont de Nemours &00., respectively, for (1) a plastic consisting of a tetrafluoroethylenepolymer, and (2) a plastic consisting of ahexafluoropropylenetetrafluoroethylene polymer. Du Pont provides toindustry three types of PEP called A, C and C-20. As described in theirTeflon bulletins, Teflon FEP A is a general purpose grade, used for heatsealing to itself or for heat bonding to other materials. Teflon FEPtype C has only one surface modified to permit cementing it to othermaterials using commercially available adhesives. Teflon FEP type C-20has both surfaces cementable. Ryan Pat. No. 3,030,290 assigned to E. I.du Pont de Nemours & Co. describes a method of making theseperfluorocarbon polymers or resin surfaces cementable by use of anelectrical corona discharge. So far as known to the present inventorbased on a search of the prior art relating to Teflon type coating andto investigation of the available technical literature the following arethe principal types of processes along these lines.

(A) The metal surface is first thoroughly cleaned by sand blasting,chemical etching, or by use of chemical solvents, either separately orin combination; followed by spraying, wiping or brushing on a finelydivided Teflon ice type material usually suspended in distilled water,and heating until the particles fuse into a film-like coating, repeatingthe procedure if desired to add more coats as thickness is desired, thenfinally baking to anneal all coats and firmly bond to metal. This methodis the one most frequently used on pipes and vessels with curvedsurfaces.

(B) On flat surfaces the procedure described in (A) may be employedfollowed by compressing with suitable pressure means, first adding aperfluorocarbon polymer film to the deposited coat and then mashing andheating.

(C) For use on either curved or flat surfaces, the metal surface isfirst prepared as described in (A), using a suitable adhesive cement tobond a film that has a specially prepared cementable surface, the filmbeing preferably a perfluorocarbon polymer such as FEP and the surfacebeing generally referred to as an etched surface. There are severalpatents in the art of etching or rendering fluorocarbon film surfacescementable, one being the Ryan Pat. No. 3,030,290 previously noted. Thecemented film is heated to the setting or bonding temperature of theparticular adhesive employed, generally somewhat less than the meltingtemperature of the fluorocarbon polymer film. The film may be cementbonded to flat surfaces by use of rolls or by simply applying the filmto the surface and heating. It is generally recognized by those skilledin the art that plastic film is difficult to bond to curved interiors ofpipe and vessels. In all these discussions the use of the word film willbe understood to mean a fluoronated or per-fluoronated hydrocarbonpolymer or du Pont Teflon or FEP. Use of mandrels, inflated bags, andthe difference in temperature expansion of Teflon like materials andmetal to obtain a compressing contact of the film to the concave curvedsurface is a common practice, in conjunction with adhesive cement. Whereno adhesive cement is used, films bonded by these means have not ingeneral proved commercially successful on concave surfaces. The processitself is expensive and limited to short lengths of pipe. Even cementbonding the film to both flat and curved surfaces is relativelyexpensive and prohibitively so for many applications, because of theinvolved preparations of surface required and the precision required inhandling very thin films. On small pipe such as 1" and A" which arecommonly used for the miles of tubing inheat exchangers in sea-waterdistillation plants, no known means has been advanced for lining withthin fluorocarbon films at a cost compatible with the economy demandedfor such installations either with the coating being applied as a filmor by the use of dispersed particles baked on.

Other current practices, not involving plastic coated metals, butclosely related to the heat exchanger tube problem, involve the use oftubes made wholly of the fluorocarbon resinous material. Du Pont offersa bundle arrangement using numerous small comparatively thick walledtubes, two listed sizes being 0.250" OD. x 0.200" ID. and 0.100" OD. x0.080" I.D. In the first tube size above listed the wall thickness is0.025" or 25 mils and in the second tube it is 0.010" or ten mils. It isbelieved that many more square feet of surface are required over metalto offset the poorer heat transfer of the fluorocarbon polymer, theadvantage being that it is absolutely corrosion proof and less subjectto fouling or scaling. These thicker tube walls are required in order toprovide reasonable working pressures, since the fluorocarbon polymersoftens greatly upon heating and loses a substantial part of its tensilestrength from degrees F. upward. Since the fluorocarbon resinousmaterial is relatively expensive as compared to metals, even corrosionresisting alloys, often costing six to ten times as much, theserelatively thick walled tubes, compared with tubes with only one or twomil coats of PEP on the inside and outside of metal tubes, are toocostly for general seawater distillation use. Other manufacturers uselimp tubes made wholly of fluorocarbons, and having thin wall PEPgenerally from about one to two mils thick. They have the same problem,of limited working pressure and must resort to involved means to supportthe tubes or keep them from entangling and giving mechanical problems.

Cost analysis of tubes and coatings: The approximate price of a 2 or 3mil baked-on Teflon coating on a tube is about ninety cents per linearfoot for inside only and about one dollar per linear foot for outsideonly. Cost for both is about $1.80/linear foot. This would amount toabout $11.25 per square foot of tube area. This baked-on coating isadmittedly porous and will not prevent corrosion, so a corrosionresistant tube such as a 90-10 copper nickel should be used. This tubein large quantities costs about 47 cents per linear foot. To have aTeflon coated 90-10 copper nickel tube, the cost would be about $2.27per linear foot of tube, or $13.40 per square foot. Since even 47 centsper linear foot for copper-nickel tube is practically prohibitive forseawater conversion distillation plants to produce Water in competitionwith most other sources since the tubes in a plant amount to nearly halfthe total plant cost, increasing this cost five fold would becommercially prohibitive despite the advantages of Teflon coating. Heatexchangers made wholly of Teflon in the tubes, using 0.10" D. tubes with0.01" wall thickness cost approximately $3.80/ square foot for the tubesonly, to which must be added cost of fabrication into a bundle. This isconsiderably cheaper than Teflon coated Cu-Ni tubes, but appreciablymore than plain Cu-Ni tubes at $2.76/square foot. Since even Cu-Ni tubesare almost prohibitive to use, thus far, pure Teflon tubes costing stillmore per square foot would be prohibitive for sea-water distillationplants despite non-corrosion and non-fouling aspects. Thus, it wouldappear on the basis of the available prior art that chemical treatmentof the water to prevent fouling is more eco nomical when all aspects areconsidered. Until now, no one has come forth with a suitable heatexchanger tube or arrangement that will permit corrosion proof,nonfouling operation at a cost less than that of Cu-Ni tubes used withscale prevention chemical treatment. This is essential if economical,competitive conversion of seawater and brackish waters to fresh Water isto be achieved. It is believed that the methods and apparatus offered inthis disclosure and in my companion patent application Ser. No. 306,183,filed Nov. 14, 1972 provide a solution to the problem of cost reduction.These cost figures will be used later in this application for comparisonfigures.

With the foregoing disadvantages of the prior art in mind some of theprincipal objects of the present invention will now be set forth.

OBJECTS OF INVENTION (A) Bonding plastic film to metal surfaces (1) Animportant object of this invention is to provide relatively inexpensivemethods of bonding both oxidizable and inert metal surfaces,particularly sheet metal, to a plastic fluorocarbon film withoutapplication of pressure to the film by outside compression means or theuse of bonding additives together with heat. Heretofore the mostsuitable, and possibly the only, fluorocarbon film for this use ishexafluoropropylenetetrafluoroethylene polymer manufactured solely by E.I. du Pont de Nemours & Co. and sold under the trade name of PEP. FEP isa heat bondable fluorocarbon with the inertness and resistance tocorrosion of the Teflon family of fluorocarbons, with the samepreferentially oil-wettability and non-adhesiveness to many otheradhesive type materials. It is offered in film with a thickness rangingfrom 0.005 to 0.02" and widths up to about 48".

(2) A further object is the provision of a method and means for bondingplastic particularly fluorocarbon polymer films to the surfaces ofmetals which are subject to oxidation at the required bondingtemperatures in the presence of oxygen, this being accomplished in anear perfect vacuum environment. Iron, many of its alloys, copper andmany of its alloys are some commonly used metals that are vulnerable tosuch oxidation. Aluminum is not oxidizable within the bondingtemperature ranges of PEP.

(3) A still further object is provision of a method and means, using anearly perfect vacuum environment, of bonding fluorocarbon or otherplastic film to metal surfaces With substantially perfect bondingcontact without entrapment of air or other gases between the film andthe metal surface, as said gases cause weakening blisters vulnerable totearing and also tend to reduce the heat transferability of film coatedmetal.

(B) Fabrication of tubing and sleeves from composite plastic-metalsheets; and more particularly fluorocarbon polymer-metal laminates (1)Another important object of the invention is the provision of acomposite tubular article, and improved means and method of making samefrom the fluorocarbon plastic-metal sheet laminate just described.

(2) A further object is the provision of a composite tube or tubulararticle and means and method of making the same with a complete range ofcoating combinations including: (a) fluorocarbon film on the inside oftube only (b) fluorocarbon film on the outside of tube only (0) andfluorocarbon film on both the inside and outside of the tube, thecomposite tube being composed of metal and fluorocarbon film only.

(3) A further object is the provision of a tube and method and means formaking same, said tube not having been offered to industry before, beingcomposed of metal ranging from a minimum of about 0.001" thicknessupward, having a fluorocarbon film coating on either or both surfacesthereof ranging in thickness from a minimum of about 0.0005" to about0.02".

(4) Another object of this invention is the provision of a compositetube and means and method for making same from any one of a variety offlexible metals and a fluorocarbin film. The metal employed is selectedto resist chemical corrosion in the environment of its use, and, ifdesired, the fluorocarbon film may be applied in sufficient layers orthicknesses to resist permeation from fluids in contact with it undergiven temperature and pressure operation conditions.

(5) Another object is the provision of a method and means ofpre-conditioning a fluorocarbon-metal laminate to prevent bonding orsticking to dies and mandrels when shaping and heat bonding into atubular article, without impairment of the bonding of the tube seam.

(6) Another object is the provision of a method of forming a compositetubular article from a fluorocarbonmetal laminate strip wherein the solebonding agent is a previously bonded layer of fluorocarbon film on eachcontacting seam surface, wherein the tube may be spirally formed fromthe strip or from a longitudinal overlap seam configuration of thelaminated strip.

(7) Another object of the invention is to provide, when forming a tubeor sleeve or any overlap seam bond of fluorocarbon-metal laminate stripslit from a sheet of this laminate and possessing raw, exposed metaledges between the two coverings of fluorocarbon film, an effective meansand method for sealing off the exposed metal edge with fluorocarbonfilm.

(8) Another object of this invention is to provide a means and method ofrendering a tube, sleeve or sheet composed of a laminate of previouslybonded fluorocarbon film to a metal sheet, cementable to other surfacessuch as the interior and exteriors of pipes or vessels, and as a heatexchanger tube being bonded to the hole in a, tube sheet.

(C) Coating metal surfaces with a plastic-metal laminate particularly afluorocarbon-metal laminate (1) The provision of a means and method ofbonding a metal surface which may be fiat, concave or convex with afluorocarbon, using heat and pressure only; using adhesive cement andpressure only; using cement, heat and pressure only, where thefluorocarbon is part of a laminate of previously bonded fluorocarbonfilm and metal sheet.

(2) The provision of an improved and less expensive method of makingmetal surfaces, and particularly the surfaces of pipes and vessels, lessvulnerable to corrosive attack and fouling with foreign depositions thanany now available, this being accomplished by bonding the same to apreviously bonded laminate of metal sheet with one or more layers ofplastic particularly fluorocarbon polymer film bonded on each side ofsaid metal sheet, with sufficient layers or thickness of fluorocarbonpolymer to be substantially impervious to corrosive fluids, all seams ofthe lami nate being adequately sealed with the fluorocarbon.

(3) The provision of a composite tube or sleeve, fabricated from alaminate of previously bonded fluorocarbon to flexible metal sheet,wherein the metal sheet core gives the composite articles suflicientstiffness or rigidity to permit retention of pro-shaping, such asfluting, to render it more adaptable to bonding to a pipe or vessel,while still sufliciently pliable to conform to the adjacent surface whensubjected to pressure just prior to bonding. This permits completeapplication of cementing agent, if desired, and complete removal of airbetween laminate and surface to be covered, thereby avoiding mechanicalfouling so common with application of limp liners. This arrangementstill permits use of comparatively thin layers of expensive fluorocarbonwithout the difficulties inherent to handling such layers when appliedalone.

(4) The provision of a method of bonding a previously bonded laminate offluorocarbon and metal sheet, to the wall of a pipe or vessel, withoutentrapment of air, interior or exterior, where both surface of thelaminated tube or sleeve are subjected to vacuum for removal of the air.After removal of air the edge or ends of the sleeve are then pressedinto firm contact with the pipe or vessel wall, air is then admitted tothe interior side only, of the laminated sleeve, thus providingapproximately one atmosphere of pressure to firmly and uniformly pressthe sleeve against the wall of the pipe or vessel. More air pressure maybe supplied if conditions warrant, together with heating to bond thelaminated sleeve to the vessel wall.

(5) The provision of a fluted configuration of the laminated sleeve in(4) to permit minimum contact of sleeve with pipe or vessel surfacefacilitating removal of air, and providing uniform conformation of thesleeve to the pipe or vessel wall when pressure is applied to it.Further, where a bonding cement is to be used, to permit uniform contactof the cementing material with both laminated sleeve and the pipe orvessel wall.

(6) The provision where a laminated sleeve of fluorocarbon film andmetal is to be cement bonded to the surface of a pipe or vessel, of amethod of circulating a thinned liquid form of the cement or dispersionof it in a gas such as air through the annular space between thelaminated sleeve and pipe or vessel wall and a method for subsequentremoval of cement solvent by circulation of air or gas, then proceedingas in (4).

My invention may be considered under the following headings:

Phase A: The preparation of metal-plastic laminates, and moreparticularly fluorocarbon-metal laminates.

Phase B: The preparation of improved composite tubes from laminates,particularly those produced under Phase A.

Phase C: Method and means for coating metal surfaces with a previouslybonded plastic film and metal sheet.

These will be considered in order.

The invention will be more readily understood by reference to theaccompanying drawings, largely diagrammatic in character, illustrativeof the improved product and method and means for producing the same.

In the drawings:

FIG. 1 is a longitudinal sectional view showing an unbonded laminate ofplastic film and thin metal superposed upon a flat base; and alsodepicts the same after bonding.

FIG. 2 is a view similar to FIG. 1 intended to illustrate the expansionand buckling of the plastic film at an intermediate stage of heating inthe course of bonding the laminate;

FIG. 3 is a view similar to FIG. 1 with the laminate superposed upon aconvexly curved metal surface;

FIG. 4 is a view similar to FIG. 2 at an intermediate stage of expansionof the plastic but with the laminate superposed upon a convex surface asin FIG. 3;

FIG. 5 is a view similar to FIG. 1 but with the unbonded laminateresting on the concave surface of a metal base;

FIG. 6 is a view similar to FIG. 5 but with the plastic layer shown atits maximum expansion as in FIGS. 2 and 4;

FIG. 7 is a view similar to FIG. 5 but with the plastic film shrunk andpulled away from the metal sheet;

FIG. 8 is a side view partly in section of a heating vessel or containersubjected to a vacuum pump or the like and having suspended therein acomposite roll of plastic and metal sheets to be subjected to a heatbonding operation under subatmospheric pressure conditions;

FIG. 9 is a transverse sectional view on line 9-9 through the compositeroll of FIG. 8 on a larger scale than in FIG. 8 and with the core shownproportionately much larger than in FIG. 8;

FIG. 10 is a longitudinal sectional view of the composite roll of FIG. 8and on a larger scale taken on line 1010 of FIG. 9 and showing thespacer strips of FIG. 8 on each end of the composite roll, the core alsobeing shown enlarged as compared with that of FIG. 8 but of somewhatless proportional size than in FIG. 9;

FIG. 11 is a diagrammatic view showing an apparatus for bonding one ormore layers of plastic film to each surface of a flexible metal strip,said apparatus including three fluid-tight vessels or containersconnected by elongated heating conduits, the whole system beingsubjected to a suitable degree of vacuum, means being provided forpassing the metal strip successively from a first vessel through a firstconduit to a second vessel and thence through a second conduit to athird vessel, plastic film being adapted to be supplied to oppositesurfaces of the metal film in continuous operation and bonded thereto byheating under subatmospheric conditions;

FIGS. 12a and 12b are further schematic views of apparatus showingalternate means for converting a plastic clad metal strip or laminateinto a finished bonded tubular article without employing any bondingadhesive other than the plastic coating itself;

FIG. 13 is a longitudinal section of a three-ply plasticmetal laminatewhich may be converted into a composite tubular article by one of themeans shown in FIGS. 12a and 12!);

FIGS. 14 and 15 are longitudinal sectional views of another form oflaminate including spaced strips, which may be converted into a plastictube by one of the means shown in FIGS. 12a and 12b;

FIG. 16 is a fragmentary cross sectional view of one of the overlappingseam portions of the three-ply tube undergoing bonding treatment;

FIG. 17 is a view similar to FIG. 16 but showing a composite two-plytube comprising a plastic metal laminate with the seam exposed forbonding as in FIG. 16;

FIG. 18 is a view similar to FIG. 17 but showing a modification;

FIG. 19 is a perspective view partly broken away with one end and anintermediate portion shown in transverse section, of a composite tubeproduced in accordance with the present invention;

FIG. is a transverse sectional view of a flattened tube produced inaccordance with my invention;

FIG. 21 is a diagrammatic view showing a schematic arrangement forpulling a pliable composite tube of plastic clad metal tubing circularin cross section through a shaping die to form a fluted tube;

FIGS. 22 and 23 are longitudinal sectional views with parts illustrateddiagrammatically of an apparatus for bonding a fluted coated tube suchas is shown in FIG. 21 to the interior of a cylindrical outer pipe orvessel;

FIG. 24 is a cross sectional view of the cylindrical vessel of FIGS. 22and 23 with the fluted sleeve shown therein but not yet bonded; and

FIG. is an end view partly in section of one end of FIG. 23 taken online 25-25 thereof.

Description of Invention PHASE ATHE PREPARATION OF IMPROVEDMETAL-PLASTIC LAMINATES This phase of the invention is illustratedprimarily by FIGS. l-11, inclusive, which illustrate the preparation ofmetal-plastic laminates including the method, apparatus for carrying outthe method, and the improved article. The preferred method relates toadhering a film of plastic material to a metal surface and includes thesteps of superposing a first lamina or layer of plastic film upon asurface of a second lamina or layer formed of thin metal and subjectingthe laminae to reduced atmospheric pressure conditions to remove any airfrom between the laminae and applying suflicient heat to soften theplastic film and bond the same to the metal surface to form a bondedmetal-plastic laminate. The metal surface may be flat or curved. Theplastic is preferably in the form of a film of fluorocarbon polymer. Themetal may be oxidizable or unoxidizable at the bonding temperature ofthe plastic. Where the plastic is a fluorocarbon polymer the bondingtemperature should be within the approximate range of 450 F. to 625 F.The laminae to be bonded may be wrapped in coils around a shaft, tube orcore and subjected to vacuum treatment while in wrapped form for thepurpose of eliminating any air. One or both sides of the metal strip orlamina may be coated with plastic film. One bonded plastic side of themetal strip may be coated with silicone or the like to prevent stickingto a support backing strip when heated.

Phase A of the invention will now be more fully described by referenceto FIGS. l-ll inclusive of the drawmgs.

FIG. 1 shows a layer 1 of heat bondable plastic film preferably offluorocarbon polymer, such as Du Pont FEP from 0.0005" to 0.02"thickness superimposed on a sheet of metal 2 from 0.0012" upward, bothlayers resting on a flat base 3. The film and metal sheet appear flat,before and after bonding with heat at 450 to 600 F. in

a vacuum.

FIG. 2 shows the film 1 and metal sheet 2 of FIG. 1 at an intermediatetemperature, 300 to about 450 F., when the film is at its maximumexpansion prior to shrinking and bonding to the metal surface as shownin FIG. 1. Air trapped under the folds of film 1 will cause bubbles orblisters upon shrinking and bonding of the film unless the process isperformed in a vacuum.

FIG. 3 shows a FEP film 1 superimposed on a sheet of metal 2, both incurved position over a curved base 4, the film being on the convex sideof the metal sheet which is, in turn, on the convex side of the base 4.The film and the metal sheet appear this way prior to any heating andafter heat bonding at a temperature of 450 to 600 F. in a vacuum.

FIG. 4 shows a FEP film 1 at its maximum expansion between 300 and 450F. prior to shrinking and bonding from 450 to 600 F. as shown in FIG. 3.

FIG. 5 shows FEP film 1 superimposed on metal sheet 2, touching itsconcave side, it in turn resting on the concave side of base 5, allprior to any heating.

FIG. 6 shows FEP film 1 at its maximum expansion between 300 and 450 F.prior to shrinking from 450 to 600 F.

FIG. 7 shows FEP film 1 shrunk and pulled away from metal sheet 2 as thetemperature is elevated above 300 F failing to bond to metal sheet 2.

FIG. 8 show a hollow cylindrical vessel 6 from which air is removedthrough conduit 15 to a source of vacuum (not shown). This vessel 6 isbuilt to permit removal of ends 6a to permit entering, by means offlanges 16. Inside 6 in a composite roll 11' having, first, a base sheetof heavier metal (about 0.01" thickness) for maintaining a true coilwhen very thin metal sheets are to be bonded to PEP, this heavier sheetshown by numeral 11. At each end of sheet 11 is a spacer strip 12 offlexible material, about to A;" thick and 1" to 2" wide and attached tosheet 11 with slack to allow for curving over sheet 11 when coiled.These spacer strips can be made of any suitable material such as wovenasbestos tape or fiber glass. Curved over 11, between spacer strip 12is, next, a layer of thin flexible metal 13 to be bonded to a FEP filmsheet. On top of metal sheet 13 in contact with it is a thin FEP sheet14 which is to be heat bonded to the metal strip 13. Since the combinedthickness of sheets 13 and 14 is only a few mils, the pace between themand the bottom side of base sheet 11 created by spacer strips 12 isample to allow for intermediate expansion of PEP 14 when it is beingbrought up to bonding temperature. The composite roll 11' is held intactby pairs of curved straps 10 bolted together at flanges 17 as shown inFIG. 9. The composite roll is secured to and supported by an axiallyextending pipe 7 which may be moved into tank 6 by means of rollersupports 8. Any of several means are employable for this purpose as thefabricator might choose. The vessel may be heated to bonding temperatureof 600 F. by any of several heating means available to those skilled inthe art, as indicated at 9.

FIG. 9 is a cross-section view of the composite roll 11' showing slot 16in pipe 7 as one of several means of securing base sheet 11 to pipe 7.As in FIG. 8, 11 is the base sheet; 12 is a spacer strip; 13 is themetal sheet to be coated; 14 is the FEP film to be heat bonded to themetal sheet.

FIG. 10 is a longitudinal cross-sectional view of composite roll 11'giving more detail of the arrangement of PEP 14 on top of sheet metal13, both on top of base sheet 11, with spacer strips 12 at each end.

FIG. 11 shows a schematic arrangement of apparatus for bonding, withheat, one or more layers of PEP film to each side of a flexible metalsheet, the whole operation carried out, without a base sheet or spacerstrips, and in a substantially subatmospheric pressure or vacuumenvironment. The term vacuum does not mean a perfect vacuum, butsuficiem vacuum to provide substantially air free bonding of PEP film tothe metal strip without use of mashing devices.

Vacuum pumps are well known in the art. Modern vacuum fore pumps mayproduce pressure down to about 0.001 mm. of mercury. Such extremepressures may be unnecessary for the purpose of the present inventionand the degree of vacuum to be employed in a given case may bedetermined by experimentation. Pressures of from 0.1 to 0.01 mm. ofmercury are generally satisfactory. A higher degree of vacuum, whilesuitable, may be ditficult to attain commercially, and a lower degree ofvacuum may leave some air between the laminae.

Three containers, preferably metal vessels capable of withstanding asubstantially complete vacuum, shown as 18, 19 and 20, are joined asshown by conduits 22 and 25. These conduits are of metal, suflicientlywide to accommodate maximum width rolls to be coated (about 4', suf.ficient depth, at least A", to accommodate intermediate expansion foldsof the PEP film). There is, preferably, a slightly convex curve on theinside bottom of the conduits. This supports the moving metal sheet toassure convex contact of the FEP film with it, prior to bonding. A flatsupport would probably suflice under some circumstances, but the curvedsupport is highly preferable. This conduit must be of suflicientstrength to withstand substantially full vacuum without internalsupports. Numeral 21 depicts a valved conduit leading to a source ofvacuum (not shown) which imposes vacuum on the whole system. The systemas shown will apply two layers of PEP film to each side of a flexiblemetal strip. The metal strip 30a from strip source shown as roll 30 incontainer 18 is pulled into conduit 22 underneath support roller 32which forces it onto the curved bottom 33 of conduit 22. PEP films 28aand 29a are superimposed upon the metal sheet from rolls 28 and 29 incontainer 18 and are held to the metal sheet by rollers 31 and 32. Theunbonded layer of metal 30a and two layers of PEP film 28a and 29a movethrough heat zone 23 (heated by any of several Well known means) wheresufficient heating is effected to bond the FEP to the metal (500 to 600F.). It should be stated here that most rolls of flexible metal shouldbe washed grease and dust free, with any, of several well knownsolvents, prior to placing in container 18 as is well known to thoseskilled in the art. This is all the preparation needed to insure a goodheat bond of the PEP to the metal.

Continuing, the metal sheet 30a with the two layers 28a and 29a of PEPbonded to it on the top surface moves through partial cooling zone 24(with certain types of fluorocarbons this cooling step may be omitted).The metal strip 30a with the two layers of bonded PEP on one side passesover guide roller 34 which also functions as a silicone applicator forcoating the bonded PEP surface with silicone or the like to preventsubsequent sticking to the curved bottom 39 of the next heating zone 26in conduit 25. The details of the silicone applicator-roller 34 are notshown as this is a common appliance known to anyone skilled in the art.It should be stated that it might require a hollow shaft, with apacking, extending outside to permit replenishing the supply of siliconeoil or the like in the roller which must be perforated to supply thesilicone to the PEP surface contacting it. The silicone applicatorroller 34 also serves to help confine the moving strip of metal and FEPto the curved bottom 33 of conduit 22, and to direct it to the upperroller 35. Rolls 37 and 38 in container 19 supply the second two layers37a and 38a of PEP film which are superimposed on the uncoated uppersurface of the metal strip 30a at roller 35. Roller 36 functions to holdthe metal sheet, with its two bonded layers 28a and 29a of PEP on theunderside now coated with a film of silicone oil or the like and its twonew layers 37a and 38a of unbonded PEP on the top side, to the convexside of curved bottom 39 of conduit 25. The metal strip 30a and the fourPEP layers pass through heating zone 26 where the two unbonded layers ontop become firmly bonded to the top surface of the metal strip, thesilicone coating on the bottom of the composite strip preventingsticking of the already bonded PEP to the hot curved base 39. The metalstrip 30a with its two bonded layers of PEP on each side is passedthrough cooling zone 27, then under guide roller 40 which serves toconfine the composite strip to the bottom 39 and also to direct thefinished strip onto roll 41 in container 20. If the composite metal-PEPstrip is to be used as lining material to be cemented to the surface ofa pipe or vessel (interior or exterior), the last layer of PEP to beadded (from roll 38) should be type C PEP with the etched side up, sothat the finished composite sheet will have one side with etched PEPexposed for cementing purposes. One sheet or layer of PEP film can beapplied with this set-up, or several as desired, adding more rolls offilm to the containers as needed. Since this would be evident to oneskilled in the art, it is not shown. The reason for using severallayers, for example two layers of 0.001" PEP film instead of one layerof 0.002" which would give the same thickness, is to avoid the hazard ofpin holes which will often exist in the film. It is not likely that twopinholes would coincide in two layers of film, whereas a single thickerlayer might have pinholes. It was found that two layers of type C PEPeach 0.002" thick bonded to 0.005" aluminum strip was invulnerable toconcentrated HCl for three weeks, but finally showed slight permeation,all at atmospheric temperature and pressure. To obtain a nearlycorrosion proof coating it is recommended that more than two layers of0.002" be used, depending on the corrosive fluid being handled and thetemperatures and pressures under which it operates. It has been foundthat aluminum strip 0.005 to 0.008" thickness, using one layer of 0.001PEP type A each side, a material cost of approximately 32 cents persquare foot, will make a A" 1D. tube with 40 lbs. working pressure at350 F. This tube would be suitable for large scale use in low operationpressure sea-water distillation systems. This tube would cost about 25to 30 cents per linear foot manufactured into a heat exchanger tube. Ifa highly corrosion resistant -10 copper-nickel thin sheet is usedinstead of aluminum, the cost per foot would increase about 10 cents tofrom about 35 to 40 cents per foot. The product is a composite tubewhich is deposit and scale resistant, corrosion resistant, fluorocarboncoated both sides with sufiicient 1 mil coating to provideoil-wettability and dropwise condensation on the steam side, and withgood thermal conductivity, which may be produced at a cost of about 40cents per foot. Aluminum may be used, by proper arrangement andmaterials combination in heat exchangers. This is a market savings ascompared with a I.D. 90-l0 Cu-Ni tube at 47 cents per foot, uncoated andsubject to scaling and fouling and not giving dropwise condensation onthe steam side. It is much less expensive than a 47 cents a foot Cu-Nitube coated inside and outside with Teflon at an added cost of $1.80 perlinear foot running its total cost to $2.27 per foot. Since the heatexchanger tubing accounts for nearly half the total cost of a sea-waterdistillation plant, providing a much better tube at 35 cents per footover 47 cents per foot would mean a reduction of approximately 25% ofthe initial cost of tubing and 11 or 12% of the total plant cost. A 30cents per foot tube would save 36% of tube cost, and a 25 cent tubewould save 47%. The novel methods depicted in this invention may be usedto produce suitable aluminum tubes coated both sides with PEP forapproximately 25 cents per linear foot, which tubing may be suitablyused with sea-water, oil field brine, brackish waters, and Great SaltLake Brines using methods disclosed in another patent application of thepresent applicant companion to this one.

A distinctive feature of the invention as set forth above is the use ofreduced atmospheric pressure conditions accompanied by heat to softenand bond the plastic film. The reduced atmospheric pressure should besutficient to remove substantially all the air from between the laminaeand the heat should be sufficient to effect bonding of the laminaewithout the application of pressure. Some of the advantages of suchtreatment will now be set forth.

Outstanding Advantages of Preceding Disclosure as to Phase A (l) The useof vacuum permits uniform and complete bonding without entrapment ofair. When vacuum is not used, a rolling device or confinement devicemust be used, as shown by Du Pont Bulletins T-l 1A and T13C. Lab:oratory tests have shown that rolling or confinement of the heatsoftened film seriously reduces its bonding strength. But even assumingthe practitioners of this have a means of keeping that bond strength,the herein described method of bonding in a vacuum is simpler, involvesless manipulation and fewer operations, and permits multiple applicationof individual films to both sides in a continuous process.

(2) The use of vacuum completely eliminates the problem of oxide filmsforming on the metal surface when heating metals such as iron, copperand their alloys. These oxides bond to the fluorocarbon and very readilyrelease from the parent metal surface, giving virtually no bond of it tothe fluorocarbon film. To overcome this obstacle, Du Pont recommends useof surface treated copper which, of course, involves another expensivestep in the operation (see Bulletin T-13C).

(3) The economic advantages are great: No bonding cements or additivesare required; less costly steps are sufficient to achieve multiplecoating both sides; achievement of multiple side coatings both surfacesof a metal strip is accomplished in a continuous operation for hundredsof feet of continuous lengths; ability to bond minimum thickness offluorocarbon film to minimum thickness metal sheet in a simpler andcontinuous manner, thereby saving the excess use of the expensivefluorocarbon polymer. Some of these are advantages over bondingfluorocarbon film to metal as done by others; the advantages over othermeans of coating metals with fluorocarbons such as spraying dispersedparticles, heat annealing and repeating to achieve multiple coats, isastronomical, usually costing about of such other processes. The presentmethod can produce a plastic-metal laminate in which the metal is coatedon both sides with plastic at a cost of 35 cents per square foot whereasthe same metal with sprayed-on baked-on fluorocarbon polymer would cost$10.00 per square foot for both sides. The least expensive metallaminate with one coat of PEP on one side found was $1.00 per squarefoot in large quantities; for both sides the cost would be $2.00 persquare foot. Applicants method costs about 16% of this latter mentionedproduct, and about 4% of sprayed-on product.

PHASE BDESCRIPTION OF INVENTION RELAT- ING TO MAKING COMPOSITE TUBESFROM PLASTIC-METAL LAMINATES What I refer to as Phase B relates to theformation of composite tubes or tubular articles from previously formedplastic-metal products or laminates and includes theimproved method offorming such composite tubes, apparatus for carrying out the method, andthe completed composite tube itself. The invention will be more readilyunderstood by reference to FIGS. 12a to 20, inclusive.

This phase of the invention, as previously indicated, relates to theformation of composite tubes or tubular articles from plastic-metallaminates such as those described under Phase A supra, and comprisesshaping such article into tubular form, leaving an exposed plastic seamportion and applying heat to bond the seam portion and complete the tubeor tubular article. The plastic film is preferably a fluorocarbonpolymer such as Teflon. The lamina is preferably passed through aconventional tube forming die to form the tube and is preferablypre-coated with a silicone lubricant to facilitate passage through thedie. The invention will be more fully understood by specific referenceto FIGS. 12a to of the drawings.

FIGS. 12a and 12b show a schematic arrangement for converting FEP orfluorocarbon clad metal strip, into tubing, with the aid of heat butwithout employing any bonding adhesives other than the fluorocarboncoating itself; in all cases where the fluorocarbon film is bonded tothe metal strip by heat prior to this step of forming into a tubulararticle or sleeve. FIGS. 12a and 12b show two methods of tube forming,each with its own possible advantages, although experimental work thusfar would definitely favor the longitudinal seam method over the spirallap seam method. The longitudinal seam tube required about 20% less flatmaterial to make a tube of the same seam overlap area, which governs thestrength of the seam, as compared to the spiral wrap tube. To make aI.D. tube, coated with plastic both inside and outside, a 3" wide stripof metal, coated both sides with plastic as shown in FIG. 13 where 43depicts a metal strip, 42 shows plastic films,

preferably FEP, on both sides, is used. Such a composite strip 53 ofmetal, coated on both sides with plastic, is pulled from roll 52 first,through silicone oil coating device 54 (not detailed because common inthe art) to coat both surfaces of the composite strip with silicone oillubricant for easier passage through shaping die and prevent sticking orbinding to mandrels in heat seam bonding apparatus. To make alongitudinal overlap seam bonded tube, silicone coated composite strip55 is pulled as into and through shaping die 56 (not shown in detail asit is known in the art) whence it leaves as an unbonded, overlap seamtube 57. It is then pulled through a heated die 58 with tolerancesufliciently restricted to slightly embed each overlapping edge into thesoftened plastic coated surface adjacent to it, thereby firmly bondingthe two strips together and sealing the raw exposed edge of metalcreated when the plastic coated sheet is slit into strips of therequired widths, in this case 3". The strip emerges as bonded tube 59that can be produced continuously in lengths equal to the length of theroll of initial material 52.

A simple cross-section view is shown at 60, showing the bonded overlapseam which in this case is about /2" wide. Tensile tests of sectionsfrom a I.D. tube made of 0.005" soft aluminum with 1 layer 0.001" PEPfilm on each side showed the overlap /2 seam bond to be much strongerthan the laminate itself. The tube wall itself failed at temperatures upto 400 F., instead of the bonded seam, when subjected to tensile strain.To make a spiral wrap tube (FIG. 12a) silicone coated plastic clad strip61 is fed from the coating device 54 onto a mandrel in step 62 (notshown in detail because common in the art) and is heat bonded in step63, removed from the mandrel at 64 and emerges as bonded spiral tube 65.Precoating the strip with silicone oil permits use of a wrap mandrel andheating of same, for otherwise it would bond to the mandrel. It has beendiscovered in this experimental work that, although silicone treatmentof a prebonded fluorocarbon film on metal will prevent it from stickingto other metal even up to 600 F., it does not have any observabledeleterious effect on bonding previously bonded to metal fluorocarbonfilms to themselves. This makes possible this very vital arrangement forusing silicone oil coatings in the manner just described. This method isbelieved to be novel as this particular manner of using a stickprevention coating has not been found in the existing art. The prior artdoes teach the use of silicone coatings on mandrels to prevent stickingof wrapped, unbonded fluorocarbon film, having no pre-coating of thefilm with silicone oil. In making this tube, use of prebondedfluorocarbon-metal laminate is vitally important, since unbondedsuperimposed layers of fluorocarbon film and metal will not suitablybond when shaped into an overlapped seam tube or in a spirallyover-lapped seam tube.

FIG. 13 shows a strip of metal 43 with fluorocarbon films 42, 42,preferably PEP, previously bonded to both sides, this one 3" wide, toproduce a tube /1" LD with fluorocarbon coating on both the inside andoutside of the tube.

FIG. 14 shows a comparatively wide sheet of metal 43 with same sizesheet of fluorocarbon film 42 previously bonded to it on one side with1" wide strips of fluorocarbon 44 bonded to the other side with 5"spacing between strips. This composite sheet is slit, as shown in thecenter of the 1 strip at 47 and in the center of the bare space betweenthe 1 strips at 48. This produces the composite strip depicted in FIG.15, comprising a strip 43 of metal 3" wide with an equal layer offluorocarbon bonded film 42 on one side, and a strip 44 of fluorocarbonbonded film /2" wide adjacent to edge of metal str1p 43 on the otherside. This strip may be passed through stages depicted in FIGS. 12a and12b to produce a I.D. metal tube similar to those shown at and 65 inFIGS. 12a and 12b with the fluorocarbon bonded film either on the insideor the outside of the tube, with exposed metal surface on the oppositeside in each instance, this all governed by manner in which it is fedinto the shaping die 56 or spiral wrapping operation in 62. Since thisprebonded fluorocarbon coat will not readily bond to raw metal ifsilicone is present (which is needed to prevent sticking to the mandrelsof other coated surfaces), the Az" strip 44 on the bare side is neededto effect a good seam bond and still permit use of the nonstickingagent, silicone.

FIG. 15 has been described in connection with FIG. 14.

FIG. 16 is a cross-sectional detail of the overlap seam and illustratesbonding of same and sealing of the exposed edge of raw metal where metalis coated on each side with prebonded fluorocarbon film to produce acomposite tube completely coated with fluorocarbon inside and outside.The metal is 43, the fluorocarbon coat is indicated at 42 and thesealing of the metal edges is shown at 45.

FIG. 17 is a cross-section detail of a composite strip including anoverlap seam 45 wherein a fluorocarbon film 42 is prebonded andcompletely covers one side of the metal strip 43. The composite stripalso includes a prebonded strip 44 on the edge of the other exposed sideof the metal strip 43, arranged to produce a tube completely coated withfluorocarbon on the inside and with no coating on the outside. The metalis depicted as 43, the full coat of fluorocarbon as 42, the strip offluorocarbon as 44, and the seal on the inside edge of metal as 45,where strip 44 bonds to coat 42.

FIG. 18 shows a cross-sectional detail of an overlap seam and bondingwhere fluorocarbon film is prebonded completely covering one side ofmetal and is a prebonded strip on the edge of the other side of themetal, and arranged to produce a tube completely coated withfluorocarbon on the outside and no coating on the inside. The metal isdepicted as 43, the complete coat of fluorocarbon as 42, the strip offluorocarbon as 44, and the seal of edge of metal as 45, where strip 44bonds to coat 42.

FIG. 19 shows a composite tube 52 made of Teflon FEP coated metal whichmay be coated with FEP on both sides or on the inside only or on theoutside only. It may be modified to permit cement bonding to theinterior of a hole in a tube sheet such as is used in heat exchangers.On each end of the tube a strip 51 of Teflon FEP C about one inch wideis wrapped in at least one layer with the etched side of the FEP on theoutside. The strip 51 should be etched on one side and wide enough tomore than equal the depth of the hole into which the tube is to bemounted. This FEP film is adhered to the tube by heating from 550 to 600F. thus readily and securely bonding the strip 51 to the convex curve ofthe tube when wrapped around it. This provides an etched surface at eachend of the tube which permits its cementing to the interior of a hole ina metal plate with use of a variety of suitable well known adhesives,such as epoxy resins. If the tube is to be used to condense steam on theoutside or change the temperature of mineralized waters, it would not bedesirable to have the tube coated with the etched side of FEP outthroughout its length as the etching tends to make it water wettable andwould defeat the purpose for which the fluorocarbon film is being used,causing it to fail to promote dropwise condensation of water or permitscale to form and cling if in contact with mineralized waters.

FIG. 20 shows an arrangement whereby additional fluorocarbon sealing ofthe tube seam may be effected, both inside and outside, if it is foundthat the seal of the edge as shown and described in connection withFIGS. 16, 17 and 18 is inadequate. Since it has been found that anuninhibited strip of FEP will bond when heated lengthwise either flat oron a surface or on a convex curved surface, strips of FEP 50 and 50' maybe bonded to the FEP-metal composite tube 49 by either mashing the tubeflat as shown, or if it is larger, mashing the seam side to flatness,placing the strip 50 and 50' on it in sequence with the FEP film restingon top of the seam joint each time, and heating and bonding. This stripprocedure would 14 be desirable, generally, when it is desired to havethe tube absolutely corrosion resistant.

Outstanding Advantages of Novel Preceding Disclosure on Tubes as toPhase B (1) The economic advantages have already been pointed out inprevious parts of this disclosure. They are enormous. In the firstplace, this provision of a comparatively inexpensive tube with a wellbonded and permanent bond of fluorocarbon film inside and outside isunique. No such tube has been offered for use to this date. Tubes linedand coated with fluorocarbons by methods used to date are prohibitivelyexpensive for the much needed use in sea-water distillation and thelike. Coating the concave surfaces of tubes with fluorocarbon film hasproved very cumbersome and expensive in larger tubes, requiring use ofconsiderable applied pressure while heating and producing a weak bondwith much trouble from air bubbles or blistering; and in smaller tubessuch as 1" diameter or less, the thin films are virtually impossible tobond to the tube interior without air bubbles or blisters. Using mymethod of bonding the fluorocarbon film to the metal in a flat or convexcurved shape as a sheet or strip, then fashioning it into a tube, usingthe fluorocarbon coat as the seam bonding medium, overcomes this problemof bonding such film to a concave surface, simply and economicallywithout use of applied pressure or cementing additives to coat or cementadditives to bond the pipe seam.

(2) This novel tube and method of making provides (again, no such tubeis yet available on the market) a very thin wall tube with very thinfilms of expensive fluorocarbon which are fully adequate for many uses,particularly heat exchanger tubes in sea-water distillation plants. Useof very thin metal sheet, five to ten mils thick, permits use of alloymetals such as -10 Cu-Ni and aluminum brass at about one fifth the costfor metal as required by conventional heat exchanger tubes of the samematerial. The metal in my I.D. tube composed of 8 mil thick 90-10 Cu-Niand 1 mil Teflon each side costs approximately 11 cents per foot of tubeas compared to more than 40 cents per foot for a 0.D. conventional tubeof this material. The 1 mil coating of Teflon FEP film on each side andthe cost of fabricating into a tube adds 25 to 30 cents per foot cost tothe tube, making a total of 35 to 40 cents per foot for a Teflon coatedand lined tube to compete with 47 cents per foot cost of finished,conventional tube with no coating of Teflon. To coat this latter tubeinside and out with a porous, less desirable coat of Teflon costs anadditional $1.80 per foot which is prohibitive for most uses.

(3) Another novel and important advantage is discovery thatfluorocarbon-metal laminate can be coated with silicone type oil andstill be bonded to itself without impairment of the bond, and stillprovide the vital function of lubrication in the shaping step andprevention of sticking in the heat bonding of the same step.

(4) Still another advantage in this disclosure is the unique means andmethod of getting a good seam bond on the tube no matter whether thetube is coated both inside and outside, or, singly, on either side withfluorocarbon film. There are instances where it is desired to have thefluorocarbon on the inside only, on the outside only, and on both sides;my method provides this variety.

PHASE CDESCRIPTIVE OF LINING PIPE OR VESSEL WITH PLASTIC CLAD METALSLEEVE This phase (C) of the invention is illustrated in FIGS. 21-25inclusive, and more particularly this phase of the invention relates tothe method of lining the interior surface of a pipe or vessel with asealed seam sleeve or tube consisting of a previously bonded laminate ofplastic film to metal heet comprising the steps of readering theinterior surface of the pipe or vessel cementable; placing inside thepipe or vessel a liner or tube whose exterior area is approximately thesame in dimensional area as the pipe or vessel interior area and whichis coated inside with a previously bonded film of plastic and whoseexterior is either a cementable metal surface or cementable previouslybonded plastic film; impregnating the interior of the pipe or vessel andthe exterior of the liner tube or sleeve with a coating of cementingmaterial; exhausting substantially all gases from both the interior andexterior of the liner to etfect subatmospheric pressure; compressing theliner to the inner surface of the pipe or vessel by applying atmosphericor greater pressure to the interior of the liner; bonding the liner tothe pipe or vessel interior by the setting or curing of the cementingmaterial, with or without the application of heat. The cementingmaterial is preferably applied as a liquid or dispersed liquid in a gasduring the impregnating step and is circulated through a closed system.

The plastic film is preferably a fluorocarbon polymer such as PEP Teflonor the like and may be a tetrafluoroethylene polymer or copolymer or ahexafluoropropylenetetrafluoroethylene polymer or copolymer.

The invention also comprises the method of lining the interior surfaceof a pipe or vessel with a sealed seam sleeve or tube consisting of apreviously bonded laminate of a plastic film to a metal sheet; saidmethod comprising the steps of cleansing the interior surface of thepipe or vessel; placing inside the pipe or vessel a liner, tube orsleeve whose exterior area is approximately the same dimensional area asthe pipe or vessel interior area and which is coated inside and outsidewith a previously bonded plastic film; creating subatmospheric pressureconditions by exhausting substantially all gases from both the interiorand exterior of the liner, tube or sleeve; compressing the liner to theinner surface of the pipe or vessel by applying atmospheric or greaterpressure and the bonding of the two with application of suitable heatfor a suitable length of time. The liner tube or sleeve is preferablyfluted by any suitable means. The invention will be more fully describedby reference to the drawings.

FIG. 21 shows a schematic arrangement whereby a pliable, composite tubeof fluorocarbon clad metal 59 is pulled through a conventional shapingdie 66 to form a fluted tube 67. The metal may be coated either insideonly or both inside and outside with the fluorocarbon polymer. Sincethis tube is preferably fluted to facilitate its use as a liner for apipe or vessel, its O.D., before fluting, should be substantially thesame as the ID. of the pipe being lined. When it is fluted, its CD. willbe considerably reduced permitting easy entrance into the pipe to belined.

FIGS. 22 and 23 show a means and method of bonding a fluted,fluorocarbon-metal laminate sleeve or tube such as shown in FIG. 21 tothe interior of a pipe or cylindrical vessel using only a cementingagent to bond, or using it in combination with heat, or using heat only,all with at least suflicient pressure to uniformly contact the sleevewith the pipe interior. The fluted sleeve 67 can be coated inside andoutside with heat prebonded fluorocarbon or it may be coated on theinside only since its purpose is to provide a fluorocarbon lining for apipe or vessel. If it is coated on both sides, it may be heat bondedwithout use of cement additives to the pipe interior. If it is coated onboth sides with the outside coat having an etched side on its exterior,then it may be cement bonded to a pipe interior. If it is not coated atall on the outside, it may be cement bonded to the pipe interiorprovided that the metal surface is prepared for such bonding which maybe accomplished in various well known and conventional manners. Amongthe several possible procedures are the following:

(a) Using a cementing agent together with heat and pressure The flutedtube 67, with the outside surface either coated with etched side outTeflon FEP C or with no coating, but with the metal surface prepared forcementing, is inserted in the pipe 68 to be lined. Mandrel housings 70and 73 provided with sealing O-rings 74 are attached to each end of pipewith sufficient set screws 72. A tapered mandrel 69 with hollow stem 71and air passageway hole 82 is forced into one end of the fluted sleeveor tube 67 just sufliciently to engage it without distorting it. Thismay be accomplished by turning a screw wheel 77, or the mandrel may beinserted in the end of the fluted sleeve when the housing 70 is placedon the pipe. A tapered mandrel 74 at the other end of the tube 67 issimilar to the mandrel 69 except that it has no hollow in its stem orair outlet hole 82. It may be provided with the same type of housing andmoving arrangement as does mandrel 69, which is not shown completely onthe drawing since it is preferably a duplicate of 70. Mandrel 74' isinserted into fluted sleeve 67 as was mandrel 69. Air under pressure isinjected from flexible pipe source 79 through valve 80 throughconnection 78 through hollow passageway 81 of stem 71 into interior ofmandrel 69. The air passes through outlet hole 82 into the interior ofthe fluted sleeve where its only escape route is through the flutedspace between mandrels 6974' and sleeve 67 at 83 and 86. The air thenenters the interior of mandrel housings 70 and 73, where it mixes withan incoming stream of cementing fluid. The incoming air is designatedthroughout by an arrow with a single spear. This cementing fluid may bean epoxy resin cement diluted ten to one with methyl-ethyl-ketone or amist of this cement atomized with air. This cementing fluid isintroduced into housing 70 through valve 100 at opening 101. The airarrangement through hollow stem 71 and mandrel outlet hole 82 is for twopurposes: (1) to maintain suflicient pressure inside the fluted sleeve67 over that in mandrel housings 70 and 73 to prevent the passage of anyof the cementing fluid to the interior of fluted sleeve 67, and (2) toact as a purging means to drive solvent from cement wet pipe interiorand fluted sleeve exterior after it is properly coated with cementingmaterial.

The air from hole 82 and the interior of sleeve 67 mixes with thecementing fluid in mandrel housings 70 and 73 and passes out with itthrough exit hole 88 of housing 73. The cementing fluid is depicted byarrows with two barbs, and passes from mandrel housing 70 through thefluted spaces between pipe 68 and fluted sleeve 67 at 84 and out at 85.The mixed air and cementing fluid leave housing 73 through conduit 89,valve 89 and conduit 90 into cement-air separator 91 (not shown indetail as common in the art). The air leaves the separator 91 throughconduit 93 leading to atmosphere and air pump 94 which repressures theair, which then passes through conduit 95 where it enters jet atomizer98. The thin liquid cement leaves the separator 91 through conduit 92and is enriched by more cement makeup entering the conduit 91 fromcontainer 96 through side conduit 97. This mixture is drawn into anatomizer 98 and re-mixed with air, and moves thence through conduit 99back to valve 100 to repeat its cycle. This method of applying cement tothe interior of the pipe and exterior of the fluted sleeve minimizeswaste of cementing material and facilitates what would otherwise be asticky and cumbersome operation. The improved method eliminatesspraying, dipping or brushing. Tests indicated that a 10 1 M-E-K dilutedepoxy cement does a good job of cementing when heated to 300 F. for anhour. After the interior of pipe 68 and exterior of fluted liner 67 arecoated with sufficient cement and the solvent driven 011? as previouslydescribed by circulating air, only, throughout the system the wholeinterior is subjected to vacuum by exhausting air from opening 102 inmandrel housing 70 through valve 103 to source of vacuum 104. Next,mandrels 69 and 74 may be forced into the fluted sleeve 67 by turningscrew wheel 77 on each mandrel housing, firmly pressing each end of thefluted sleeve to the pipe interior. Next, atmospheric pressure isadmitted to interior of fluted sleeve, flattening the flutes and firmlypressing it to the interior of the pipe with no possible entrapment ofair between the sleeve and the pipe as it was all exhausted by vacuum.Next air is admitted to the interiors of both mandrel housings 70 and 73by Opening valves 89 and 100. In order to utilize the more intricatemandrel housings 70 and 73 to the fullest, they may then be replaced bymandrel plugs 105 and 106 as shown in FIG. 23, held firmly into thesleeve pipe by tie rods 114 and strips 112 and 113 as shown in FIGS. 23and 25. This permits addition of air under pressure through valve 108(FIG. 23), opening 109 and outlet 110 in mandrel plug 105 into theinterior of composite pipe 68 containing the sleeve '67. The properpressure is governed by conditions peculiar to the size of pipe andother variables and may be determined by those skilled in the art. Insome cases atmospheric pressure may prove sufficient. The pipe 68 withits cemented liner or sleeve 67 pressed firmly against its interior withits mandrels 105 and 106 is then placed in an oven 115 and heated tobonding temperature of the particular cement for a length of time suitedto that particular temperature. With epoxy resin cement the time shouldbe about one hour at not over 300 F.

(b) Using cementing agent and pressure only Repeat steps of (a) omittingthe final step of heating, but allowing more time for the cement to bondand cure, to be determined by trial and error. With epoxy cement atleast 24 hours will be required.

(c) Using cementing agent with heat only atmospheric pressure againstcemented liner [Repeat steps of (a), omitting final steps of usingmandrel plugs 105 and 106, but heating in oven 115 for required time andtemperature to obtain good bonding.

((1) Using cementing agent only Carry out the process as set forth undersupra, but omitting the final heating step.

(e) Use of no cement, bonding with heat and pressure only The flutedsleeve 67 must have an exterior and an interior coating of fluorocarbon.Repeat the steps of (a) supra, but omitting the first steps ofimpregnating with cement, then use the same procedure including heatingin an oven, using sufficient pressure and temperature and time to securea good bond of fluorocarbon (preferably Teflon PEP) between sleeve andpipe interior. Using FEP the bonding temperature should preferably bebetween about 575 to 625 F. for at least ten minutes after the pipe andsleeve have reached the bonding temperature. The required pressureshould be from about 50 to 200 lbs. per square inch, the exact pressureto be determined by trial and error in a particular case.

(f) In some instances heat and atmospheric pressure only may besuflicient for bonding FEP coated liner to pipe interior where vacuum isused as in all the preceding steps described. This, too, may bedetermined by trial and error.

Outstanding Advantages of Preceding Novel Disclosure 1) Utilizes novelobservation that, whereas, fluorocarbon films such as heat bondable FEPare very difficult to bond to concave surfaces, generally requiringconsiderable application of pressure during the heat bonding process,previously bonded fluorocarbon film to metal bonds quite readily toconcave surfaces with application of minimum pressure or even merecontacting of the laminate to the metal surface during the heat tosoftening temperature of the plastic. This novel approach provides aneconomical, simple means of coating the interior concave surface of apipe or vessel with a fluorocarbon film as a laminate with or withoutcementing.

(2) Use of vacuum between the laminate and the pipe or vessel interiorassures uniform and complete contact with no entrapment of air or gases.

(3) Novel apparatus for use of vacuum also utilizes vacuum for immediateand simple application of pressure to the interior of the laminatesleeve or liner to firmly contact it to the pipe or vessel interior.

(4) Novel apparatus and method for circulating thinned cement or gasdispersed cement mist to the surfaces to be cemented is convenient,economical in pre-= venting waste of cementing material, and timesaving.

(5) Fluting of the liner prior to insertion is made possible by use ofstiffened laminate (as contrasted to pure fluorocarbon thin liners whichcannot be shaped by bending), this fluting being very beneficial to giveproper positioning of the liner in the pipe or vessel, better access foruniform coating with cement, facilitate removal of air with vacuum, andassure uniform conformation of the liner to the pipe interior whenpressure is applied.

The invention has been described in detail for the purpose ofillustration but it will be obvious that modifications and variationsmay be resorted to without departing from the spirit of the invention inits broadest aspects as will be apparent to those skilled in the art.

For example while I have found the invention particularly applicable toheat bonding fluorocarbon polymer plastic films to metal films to form aplastic-metal laminate the invention in its broadest aspects isapplicable to the bonding of other plastic polymer films to metal sheetsor films. Also while I have found silicone oils to be particularlyeffective as non-sticking agents or lubricants in connection withcertain phases of my invention heretofore described other non-stickingagents or lubricants may be used within the scope of my invention in itsbroadest aspects. Also where reference is made in the specification tofeet it will be understood that linear feet are intended unlessotherwise specified.

What is claimed is:

1. The method of forming a composite fluorocarbonmetal tube whichcomprises shaping into an article of tubular form a lubricated strip ofpreviously bonded fluorocarbon plastic-metal laminate formed by heatbonding a fluorocarbon plastic to a metal strip without the use ofbonding additives, said tubular article including:

(1) an unbonded, overlapping seam portion of laminate with opposingfluorocarbon plastic surfaces,

(2) exposed surfaces of fluorocarbon plastic subject to contact withunlike surfaces of molds, dies or mandrels,

(3) a coating of silicone lubricant material applied to both sides ofthe laminate strip prior to shaping, such material functioning both as alubricant for the shaping step and as a means of preventing adherence ofthe tubular article to any unlike contacting surfaces during asubsequent heating and bonding step, while permitting uninhibited heatbonding of the seam surfaces,

then, after the aforementioned shaping of the tubular article, applyingheat and firm contact to the unbonded seam to effect full bonding ofsame without adherence of any finished tube surface to other contactingsurfaces.

2. The method according to claim 1 wherein the laminate is shaped totubular form by passing through a conventional tube-forming die.

3. The method according to claim 2 wherein the laminate is afluorocarbon-metal laminate and is previously coated on both sides witha silicone type oil to facilitate its passage through a tube forming dieand prevent bonding of this tube to a subsequent heated seam bonding dieand mandrel; and wherein the silicone coating does not interfere withthe bonding of the two previously metal bonded fluorocarbon surfaces.

4. The method according to claim 1 wherein the tubular article is coatedwith fluorocarbon film on both the inside and outside, being fabricatedfrom a laminate strip with a full coating of previously bondedfluorocarbon on each side of a metal core.

5. The method according to claim 1 wherein the tubular article is coatedwith fluorocarbon film on the inside, only, being fabricated from alaminate strip with previous ly bonded full fluorocarbon coat on oneside and a narrow margin strip of previously bonded fluorocarbon on theother side of a metal core, said narrow strip of fluorocarbon acting asa bonding agent to the edge of the fully coated side.

6. The method according to claim 1 wherein the tube is coated withfluorocarbon film on the outside, only, and is fabricated from alaminate strip with previously bonded full fluorocarbon coat on one sideand a narrow margin strip of previously bonded fluorocarbon on the otherside of a metal core, said narrow strip of fluorocarbon acting as abonding agent to the edge of the fully coated side.

7. The method according to claim 1 wherein both inside and outsideexposed metal edges of a metal core of the laminate, formed into a tubeby bonding overlapping edges, are sealed over with fluorocarbon byslight embedding of each edge into the heat softened fluorocarbonsurface adjacent to it which is effected by passage through a closetolerance heated die.

8. The method according to claim 1 wherein the tubular article includesa metal core having an inside exposed metal edge, and wherein the insideexposed metal edge of the metal core of the laminate, formed into atubular form by bonding overlapping edges, is sealed over thefluorocarbon by slight embedding of the edge into the heat softenedfluorocarbon surface adjacent to it, this being effected by passagethrough a close tolerance heated die.

9. The method according to claim 1 wherein the tubular article comprisesa metal core having an outside exposed metal edge and wherein theoutside exposed metal edge of the metal core of the laminate, formedinto tubular form by bonding overlapping edges, is sealed over withfluorocarbon by slight embedding of the edge into the heat softenedfluorocarbon surface adjacent to it, this being effected by passagethrough a close tolerance heated die.

10. The method according to claim 1 wherein the laminate is fed as astrip into a tube forming mechanism producing a tubular article with anunbonded, longitudinal, overlapping seam, then passing the tubulararticle through a heated die to firmly bond the seam by softening andwelding two fluorocarbon surfaces together, producing a finished tube.

11. The method according to claim 1 wherein the laminate is fed as astrip into a tube forming mechanism producing a spirally wrapped tubeabout a mandrel, with an unbonded, spiral, overlapping seam to produce atubular article, then passing the tubular article through a heating zonewhich softens and welds the two contacting surfaces of fluorocarbon onthe overlapping seam; the article being removed from the mandrel as afinished tube.

12. The method according to claim 8 wherein the laminate is in stripform and is coated with a silicone type oil prior to shaping into atubular shape.

13. The method according to claim 11 wherein the laminate strip iscoated with a silicone type oil prior to wrapping about a mandrel.

14. The method according to claim 1 wherein the previously bondedfluorocarbon plastic-metal laminate is prepared by heat bonding aplastic film of fluorocarbon to a metal strip in an environment ofreduced pressure without application of pressure to the outer surface ofthe plastic film and without use of bonding additives.

15. The method according to claim 1 wherein the lubricant material is asilicone oil.

16. The method according to claim 1 wherein the plastic materialcomprises a tetrafluoroethylene polymer.

17. The method according to claim 1 wherein the plastic materialcomprises hexafluoropropylenetetrafluoroethylene.

References Cited UNITED STATES PATENTS 3,673,054 6/1972 Wright et al.156272 3,660,194 5/1972 Hoffmann et al 156--218 3,700,524 10/1972 Sato1562l8 3,268,620 8/1966 Tarwid 113-120 A 3,360,157 12/1967 Bolt et a1l13120 A 3,090,717 5/1963 Raczynski et al 156-272 3,551,232 12/1970Thompson 156286 3,148,896 9/1964 Chu 285-55 3,411,542 12/1968 Walsh etal 156-218 3,452,133 6/l969 Bratton et al 156-85 CHARLES E. VAN HORN,Primary Examiner F. FRISENDA, JR., Assistant Examiner

